For optical transport network equipment, the use of a reconfigurable optical add/drop multiplexers (ROADMs) can flexibly expand the network capacity and reduce the operation cost. A wavelength selective switch (WSS) is one choice of technology for current RODAMs. For a 1×N WSS, 1 is a common (COM) port and N represents the branch ports. The WSS operates such that when a group of the WDM signals enter from the COM port, the signals are separated by optical wavelengths, and then according to the system requirement, each wavelength is routed to one of the N branch ports. Conversely, the optical signals can be received as input from N branch ports and sent as output from the COM port.
A ROADM provides an automated mechanism to flexibly add capacity as needed without resorting to expensive and service-interrupting “forklift” upgrades. A benefit of the ROADM network is its ability to add dynamic capacity wherever and whenever needed, with the assurance that the underlying network automatically compensates for the added traffic. This eliminates the need for manual tuning or wholesale upgrades. The ROADM can provide add/drop functions in multiple directions with multiple wavelength channels, and thus is suitable to achieve multi-directional interconnections between network rings and to build up mesh networks.